1. Field of the invention
The present invention relates to an apparatus for and method of controlling the idling of an automobile engine.
2. Description of the related Art
An automobile engine is frequently operated in an idling state. The idling engine speed of the automobile engine is not fixed to a certain value, but is varied in accordance with various conditions of the automboile, and targeted idling engine speeds are set in advance in accordance with the respective conditions. For instance, when the temperature of engine cooling water is below a predetermined level, the idling engine speed is increased in such a manner that the cooling water temperature promptly reaches the predetermined level. In this case, the targeted idling engine speed is set in correspondence with the cooling water temperature. When an air-conditioner is turned on, the idling engine speed is increased to rotate the compressor of the air-conditioner. The targeted idling engine speed in this case is set in correspondence with the cooling water temperature and the load of the air-conditioner. If the automobile is provided with an automatic transmission, the idling engine speed is varied in accordance with the position of a selector. The targeted idling engine speed at this time is set in correspondence with the cooling water temperature and a load applied to the automatic transmission. The engine speed is returned to the idling engine speed when the cooling water temperature reaches a set level, when the air-conditioner is turned off, or when the selector of the automatic transmission is returned to the neutral position. Control of these operations is generally effected by feed back control.
An apparatus for effecting feedback control is disclosed in Japanese Patent Unexamined Publication No. 160138/1980. This apparatus comprises an ISC valve for supplying air to a combustion chamber of an engine disposed in a bypass line bypassing a throttle valve; a plurality of sensors, including an idle switch for detecting the amount of opening of the throttle valve, an airflow sensor for detecting the flow rate of air supplied to the throttle valve, an engine speed sensor for detecting an engine speed, and a water temperature sensor for detecting the cooling water temperature; and a microcomputer which selects a targeted idling engine speed using the values detected by these sensors and varies an intake air flow rate by actuating the ISC valve so that the engine speed becomes the targeted idling engine speed, and which varies the rate of fuel injected from a fuel injector.
A power steering system is included among auxiliary equipment of an automobile. The power steering system reduces the required manual steering force by means of a booster making use of the negative pressure of the engine. This system applies a large load to the engine in comparison with the air-conditioner or other auxiliary equipment. In particular, the maximum load is applied to the engine when a steering wheel is operated to a point close to its operatable limit when the automobile is at a standstill. For this reason, if the steering wheel is operated to such a point when the automobile is at a standstill, the idling engine speed drops substantially below a set value, possibly resulting in the stalling of the engine. To prevent this engine stall, the performance of the power steering system is controlled in the prior art. In other words, when the automobile is at a stop, the operatable range of the power steering system is reduced so that an excessive load is not applied to the engine, thereby preventing engine stall. It is the time when the automobile is at a stop or is moving very slowly that a large operating range of the steering wheel is required. It is very inconvenient to reduce the operatable range at that time. The apparatus disclosed in the aforementioned Japanese Patent Unexamined Publication No. 160138/1980 does not disclose any measure for coping with the power steering system.